1. Field
The present invention relates to a semiconductor device having a stable gate structure, and a method of manufacturing the same. More particularly, the present invention relates to a semiconductor device, in which a gate structure having a fine gate foot having a length of 0.2 μm or smaller and a gate head having a predetermined size is stabilized by increasing an area of the gate foot, and a method of manufacturing the same.
2. Discussion of Related Art
According to development of IT technology, high-integration, high rate operation, a high voltage, a high power density, and the like of semiconductor devices become important. In the case of High Electron Mobility Transistors (HEMTs), which are GaN devices, among the semiconductor devices, a field effect transistor has risen as a high rate and high power device.
For the high rate operation of the semiconductor device, a gate length needs to be decreased. However, when the gate length is decreased, resistance is increased, so that there is a problem in that a high frequency characteristic deteriorates. Further, as integration of the semiconductor device is increased, a distance between a gate and a drain is decreased, so that a breakdown voltage is decreased. Further, a width of the gate needs to be increased in order to improve a power density, so that there is a possibility in that a gate collapses.
In order to solve the problem, in the case of the high rate, in order to decrease the gate length, a gate structure, in which a gate foot is small and a gate head is relatively large, has been used. Accordingly, a gate shaped like “T”, “Y”, and a mushroom is mainly used.
Further, in order to solve a decrease in a breakdown voltage generated due to a decrease in the distance between the gate and the drain for the high rate operation, a method of increasing a breakdown voltage by using a gamma (Γ) shaped gate and field plate is used. The gamma (Γ) shaped gate has a shape in which a foot portion of the gate is narrow, and a head portion of the gate elongates in one direction. The gamma (Γ) shaped gate may decrease entire resistance of the gate due to the wide head portion, and creases a depleted layer between the head portion of the gate and the drain, thereby increasing a breakdown voltage between the gate and the drain. Accordingly, the gamma (Γ) shaped gate is actually and mainly used, but in this case, the large and wide gate head is laid on the narrow gate foot, so that the gamma (Γ) shaped gate also has an unstable structure. Particularly, when the gate head is asymmetrically laid on the center gate foot, reliability during or after the process of the semiconductor is largely influenced. FIG. 1 is an SEM picture after the semiconductor process is ended, and illustrates the gate which partially collapses due to the asymmetric gate head.
In actual, a device having a high power density in a single area is demanded, and in this case, the width of the gate may be increased. When a width of a unit gate is increased as a frequency is increased, a frequency characteristic of a device is slightly decreased, and there is a problem in stability due to the increased width of the gate. That is, this phenomenon is clearer when the unit gate having the width of several hundreds of μm having the narrow gate foot of 0.2 μm stands while being dependent only on the gate foot. While the gate foot of the device operated at a low frequency is stable, a nitride-based semiconductor device having a foot of 0.2 μm or smaller is manufactured so as to be in maximal contact with air without using a dielectric material based on SiNx in order to remove a parasitic component between the gate and a substrate, and in this case, the problem becomes more severe.
In the meantime, the gate having the aforementioned structure is manufactured by a technology of forming a photoresist having a two or three layer structure, and forming a gate through etching by a difference in sensitivity of each layer. FIGS. 2 and 3 are diagrams of a process of manufacturing a semiconductor device according to the related art. Referring to FIGS. 2 and 3, first, a source electrode 21 and a drain electrode 22, which are spaced apart from each other, are formed on a substrate 10. Next, when the source electrode 21 and the drain electrode 22 are formed on the substrate 10, a first photoresist 31 and a second photoresist 32 are formed. In this case, the photoresist 31 and the second photoresist 32 are photoresists for forming a pattern in the process of manufacturing the semiconductor, and when the photoresist 31 and the second photoresist 32 are formed, a gate pattern is formed by etching the photoresist 31 and the second photoresist 32, and a metal material is deposited on the gate pattern, and then a gate electrode 40 is formed. The semiconductor device formed as described above has the gate electrode 40, in which a gate foot between the source and drain electrodes 21 and 22 has a length of 0.2 μm or smaller for a high rate operation, and a gate head is relatively larger than the gate foot as illustrated in FIG. 4.
A shape of the gate formed as described above has the head portion with a large length and the foot portion with a small length, and when the gate has a shape of “T”, the gate is called a T-shaped gate (T-gate), and the gate has a shape of gamma “Γ”, the gate is called a Γ-shaped gate. The technology of forming the gate in the related art adopts E-beam lithography in order to meet a minute design rule.